1. (Field of the Invention)
The present invention relates to a hydraulic winch for driving a winch drum by means of a hydraulic motor.
2. (Description of the Related Art)
Conventionally, a hydraulic winch mounted on a crane or the like is generally provided with a free-fall operating mode separately from a power operating mode for winding up-and-down a load (hanging goods) by means of a motor whereby a winch drum is rotated down by the load in the free-fall operating mode to freely lower the load (see Japanese Patent Application Laid-Open No. 9-216793 Publication which is hereby fully incorporated by reference).
The constitution of the conventional hydraulic winch provided with the free-fall operating mode as described above will be explained hereinafter with reference to FIGS. 28 to 31.
FIG. 28 schematically shows the constitution of a winch main body portion. In this figure, reference numeral 1 designates a winch drum, and reference numeral 2 designates a hydraulic motor (hereinafter referred to as a winch motor) as a drive source for the winch drum 1. A planetary gear mechanism 3 for performing power transmission is provided between an output shaft 2a of the winch motor 2 and the winch drum 1.
Reference numeral 4 designates a sun gear of the planetary gear mechanism 3, 5 a planetary gear, 6 a ring gear provided in the inner periphery of the winch drum 1, 7 a carrier for supporting the planetary gear 5, 8 a carrier shaft, and 9 a multidisk provided on the carrier shaft 8. The multidisk 9, a pressure plate 10 for actuating (pressing) and deactuating (alienating) the disk 9, a brake cylinder 11 for driving the pressure plate 10, and a pressing spring 12 constitute a hydraulic brake and a clutch in one 13 for connecting the winch drum 1 to and separating it from the output shaft 2a of the motor and braking the free-fall rotation of the drum 1.
The multidisk 9 comprises a plurality of inner plates (a first frictional plate) 14 . . . mounted on the carrier shaft 8 integrally rotatably and axially movably, and a plurality of outer plates (a second frictional plate) 16 mounted on a brake casing 15 in a state of being axially movably and non-rotatable with respect to the inner plates 14. When both the inner and outer plates 14 and 16 are pressed between one side wall 15a of the brake casing 15 and the pressure plate 10, the brake (clutch) is turned on, and when they are separated, the brake (clutch) is turned off.
The pressing spring 12 is provided between the other side wall 15b of the brake casing 15 and the pressure plate 10 to apply a spring force in a direction of turning on the brake to the pressure plate 10.
The brake cylinder 11 has a dual-rod type piston 11P, a positive-side oil chamber 11a for pressing the pressure plate 10 in a direction of turning on the brake (in a right direction in the figure), and a negative-side oil chamber 11b for pressing the pressure plate 10 in a direction of turning off the brake (in a left direction in the figure). A negative line 17 connected to the negative-side oil chamber 11b is directly connected to a brake hydraulic source 18.
On the other hand, a positive line 19 connected to the positive-side oil chamber 11a is branched into two lines through a high pressure selection valve (a shuttle valve) 20, one branched line and the other branched line being connected to the hydraulic source 18 or a tank T through an electromagnetic type mode switching valve 21 and a brake valve (a reduction valve) 22, respectively.
The mode switching valve 21 is switched between a brake position a and a free-fall position (a brake release position) b by operation of a mode switching switch not shown, so that the positive-side oil chamber 11a is connected to the hydraulic source 18 at the brake position a and to the tank T at the free-fall position b, respectively.
The brake valve 22 is operated by a pedal 23, and a secondary pressure according to an operating amount thereof is supplied to the positive-side oil chamber 11a of the brake cylinder 11 through the high pressure selection valve 20.
With this constitution, the following operations are obtained:
1 In the state that the mode switching valve 21 is set to the brake position a, both the side oil chambers 11a and 11b of the brake cylinder 11 are in the same pressure, and therefore, thrust is not generated in the brake cylinder 11 in itself but the pressure plate 10 along with the brake cylinder 11 is pressed by the spring force of the pressing spring 12 toward the multidisk 9 (in the direction on which brake exerts) to turn the brake on.
In this state, the carrier shaft 8 remains to be non-rotatable so that the turning force of the winch motor 2 is transmitted to the winch drum 1 through the planetary gear mechanism 3, and the winch drum 1 rotated to be wound up or down according to the operation of a remote control valve not shown.
2 When the mode switching valve 21 is switched to the free-fall position b, the positive-side oil chamber 11a of the brake cylinder 11 comes in communication with the tank T to generate a pressure difference between the positive-side oil chamber 11a and the negative-side oil chamber 11b, and the thrust of the brake cylinder 11 exceeds the spring force of the pressing spring 12 due to the pressure difference whereby the brake cylinder 11 is pressed in the direction opposite to the multidisk 9 (in the direction of releasing the brake) to turn the brake off.
In this state, the carrier shaft 8 is fee so that the winch drum 1 assumes a state capable of being freely rotated in the winding-down direction due to the load, that is, a state capable of achieving the free-fall.
When at this time, the brake valve 22 is operated, the multidisk 9 is turned on due to the secondary pressure according to an operating amount thereof, and the brake force exerts on the winch drum 1.
On the other hand, the concrete constitution of the body portion of the hydraulic winch of this kind is shown in FIGS. 29 to 31, in which the same parts as those used in FIG. 28 are indicated by the same reference numerals.
A positive-side rod 24 and a negative-side rod 25 are integrally provided on one side of a piston 11P and on the opposite side thereof, respectively.
Both the side rods 24 and 25 are formed to be hollow shafts, and a pressure plate 10 is mounted on the extreme end of the negative-side rod 5 through a connecting plate 26.
Reference numerals 27 and 27 designate bolts for mounting a pressure plate, and 28 designates an inner plate mounting body secured to the outer circumference of a carrier shaft 8. Inner plates 14 . . . of a multidisk 9 are axially movably mounted in the outer periphery of the mounting body 28.
A positive-side oil chamber 11a and a negative-side oil chamber 11b of the brake cylinder 11 are formed between a cylinder end plate 29 and the piston 11P and between the piston 11P and a side wall 15b of a brake casing 15, respectively, and connected to a positive line 19 and a negative line 17 through oil paths 30 and 31.
However, the aforementioned conventional hydraulic winch has the following problems:
(I) Overstroke of the piston 11P in the brake cylinder 11:
As shown in an enlarged scale in FIG. 30, the pressure plate 10 is provided in its center with a fitting hole 10a, in which a connecting plate 26 is fitted.
The connecting plate 26 is provided on one end thereof with a collar-like portion 26a, and in the state that the collar-like portion 26a stops at the peripheral edge portion of the fitting hole 10a of the pressure plate 10 from the multidisk 9 side, the pressure plate 10 is connected by means of bolts 27 and 27 to the piston 11P of the brake cylinder 11 (and both the rods 24 and 25).
Thereby, the cylinder thrust in a brake-off direction is transmitted to the pressure plate 10 through the connecting plate 26, whereas the spring force in a brake-off direction of the pressing spring 12 is transmitted to the piston 11P through the pressure plate 10 and the connecting plate 26.
The outside diameter dimension .phi.1 of the negative-side rod 25 in the brake cylinder 11 and the body diameter dimension .phi.2 of the connecting plate 26 are formed to be substantially equally, and both the dimensions .phi.1 and .phi.2 are set to be smaller than the fitting-hole diameter dimension .phi.3 of the pressure plate 10.
Accordingly, the negative-side rod 25 and the connecting plate 26 are free in the direction of the multidisk 9 (in the right direction in the figure) with respect to the pressure plate 10.
Because of this, when the mode switching valve 21 in FIG. 28 is switched from the free-fall position b to the brake portion a so that the pressure plate 10 is pressed toward the multidisk 9 by the spring force of the pressing spring 12, and the negative-side rod 25 and the connecting plate 26 along with the pressure plate 10 move toward the multidisk 9, overstroke occurs due to the inertia. Subsequently, when the mode switching valve 21 is switched from the brake position a to the free-fall position b, the movement of the piston 11P is delayed by the overstroke to deteriorate the switching responsiveness, thus lowering the working efficiency.
(II) Contact resistance of the multidisk 9:
When the mode switching valve 21 is set to the brake position a, the pressure plate 10 moves from the position indicated by the solid line in FIG. 31 toward the multidisk 9 as indicated by the imaginary line in the figure whereby both the inner and outer plates 14 and 16 are placed in pressure contact.
When the mode switching valve 21 is switched from the aforementioned state to the free-fall position b, the pressure contact force between both the plates 14 and 16 is released, but since the force for positively alienating them does not act, both the plates 14 and 16 still remain in the contacted state.
Accordingly, even during the free-fall operation, a small brake force caused by contact resistance is to act.
In this case, if the load weight is large, the small brake force can be disregarded. However, when the load weight is small (for example, only at the time of empty hooking during the crane operation), the load becomes slow in falling speed or is not lowered, thus lowering the efficiency of free-fall work.
(III) Free-running resistance of a wet type clutch:
When a frictional type multidisk 9 is used for the hydraulic brake 13, there possibly occurs a fade phenomenon in which a frictional coefficient of a frictional surface lowers due to heat to lower a brake force.
In such a case as described above, a wet type brake system has been employed in which cooling oil is introduced and circulated in the multidisk 9 (for example, see Japanese Patent Application Laid-Open No. 9-100093 Publication, which is hereby fully incorporated by reference).
However, according to the wet type brake, even in the case where during the free-fall operation, the pressure contact between both the inner and outer plates 14 and 16 in the multidisk 9 is released (or a clearance is secured between both the plates), the free-running resistance (drag resistance) exerts as the brake force on both the plates 14 and 16 due to the viscous resistance of cooling oil which is present between both the plates.
The brake force caused by the free-running resistance is not so large similarly to the contact resistance between both the plates, and poses no problem at the time of large load, but at the time of small load, the free-fall lowering speed lowers or an impossible lowering results.
As a countermeasure, it is contemplated that a sufficiently large clearance is provided between both the plates 14 and 16 at the time of free-fall operation. In doing so, when the load is small, the positive free-fall operation becomes enabled while the stroke necessary for pressure contact and release of both the plates 14 and 16 becomes so large that the brake responsiveness lower, thus being disadvantageous particularly in the operation for large loads such as an impossible sudden stop.
(IV) Arrangement of a high pressure selection valve:
According to the well known art in which when in the free-fall operation, the secondary pressure of the brake valve 22 is supplied to the positive-side oil chamber 11a of the brake cylinder 11 through the high pressure selection valve 20 to act the brake force, that is, according to the winch constitution in which a trouble factor such as the high pressure selection valve 20 is present between the brake valve 22 and the positive-side oil chamber 11a, a trouble or a failure in operation of the high pressure selection valve 20 occurs, and the secondary pressure of the brake valve cannot be properly transmitted to the positive-side oil chamber 11a, possibly resulting in that the braking operation as intended by an operator cannot be carried out.